Oil and gas wells normally have several strings of casing of differing diameters cemented in the well. Each casing string is made up of joints of pipe have threaded ends secured together. A typical casing joint has external threads on its upper and lower ends. A casing collar with internal threads secures the threaded ends together. In larger casing diameters, a casing collar with internal threads may be affixed, such as by welding, to one end of each pipe, the other end having external threads. Normally, the operator relies on the friction of the made-up joint preventing the threaded connectors from loosening while running the string into the well. With larger diameter casing, say from 18⅝ inch to 36 inch, the friction of the made-up connector may be inadequate to prevent loosening while running the casing.
In the past, operators have employed anti-rotation keys to prevent loosening. A rectangular pocket or slot is machined on the outer surface of the male connector. The female connector has an annular inner wall that surrounds the portion of the male connector containing the pocket. After making up the connector, the workers will drive a key into the pocket. The key has a slightly greater thickness than the distance from the base of the pocket to the inner wall, resulting in an interference fit. Normally, the workers drive the key into place with a hammer.